1. Field of the Invention
The present invention relates to a wheel shaft supporting apparatus installed in a front portion of a wheel slide of a grinding machine, especially of a cylindrical grinding machine.
2. Description of the Related Art
It is well known for a grinding machine to support a wheel shaft at both sides thereof to enforce supporting stiffness for a grinding wheel, for example it is disclosed in Japanese patent laid-open publication No. S59-161265. In this well known grinding machine, both sides of the wheel shaft mounting a grinding wheel at center is supported respectively and rotatably by right and left hydrostatic fluid bearing devices, one of hydrostatic fluid bearing devices has a hydrostatic thrust bearing mechanism. It is well known technology for a grinding machine supporting a grinding wheel at both sides of the wheel shaft to change the grinding wheel mounted at center on the wheel shaft, for example this technology is disclosed in Japanese patent laid-open publication No. H6-47662 or No. H6-47663. In these well known grinding machines, a pair of wheel shafts disposed at each side of the grinding wheel supports rotatably the grinding wheel especially by a hydrostatic fluid bearing device, and it equips a combining means coupling the opposite ends of both wheel shafts. In order to disassemble the grinding wheel, the combining means is operated into non-combining state thereby to apart one wheel shaft from the other wheel shaft so that the grinding wheel is ready to be removed. The combination of these opposite end of both wheel shafts is performed in such a manner that a taper cone projected from the end surface of one wheel shaft is inserted into a taper inside opening of the other wheel shaft and a screw ring screwing the outer end surface of the one wheel shaft secures the taper cone to the taper inside opening.
However in the well known grinding machines in abovementioned second and third related art, since the combining means of the one and the other wheel shafts is performed by the taper cone and the taper inside opening, therefore high accurate repeatability of coincidence between each center line of both wheel shafts can not be achieved when both wheel shafts are reassembled again because of changes in a taper surface fitting between the taper cone and the taper inside opening so that it is difficult to increase coupling stiffness between the wheel shafts. Further, since the grinding wheel is fitted tightly by a vertical surface fitting between the grinding wheel and a flange and a position of the vertical surface fitting is apart from the taper surface fitting between the taper cone and the taper inside opening in the well known grinding machine, therefore high accurate repeatability of coincidence between each center line of the grinding wheel and both wheel shafts can not be achieved when a new grinding wheel and both wheel shafts are reassembled again so that it is difficult to increase stiffness of the grinding wheel, too. And also, since the screw ring and a matching screw portion of the outer end surface of the one wheel shaft are exposed outside from the one wheel shaft in the well known grinding machine, the invaders such as ground pieces, grinding particles, coolant, etc act to pollute and corrode the screw ring and screw portion thereby not to operate the securing at the assembling and disassembling process after long term operation because the grinding wheel comprising a cubic boron nitride (CBN) can be operated for long term. More over, since a motor for the grinding wheel is arranged in a line of an axis of the grinding wheel in the well known grinding machine, it can happen that the motor for the grinding wheel interferes other components of the grinding machine where a diameter of the grinding wheel is smaller than that of the motor thereby to prevent from equipping the grinding wheel with the smaller diameter which is easy to be changed. Further more, since a position in thrust direction of the wheel shaft is affected by thrust bearing accuracy of an output shaft of the driving motor and positioning accuracy of a coupling combining the output shaft of the motor with the wheel shaft, the positioning accuracy of the output shaft, in other word a positioning accuracy of the grinding wheel in the thrust direction is worse to prevent from machining a workpiece into high accuracy in the thrust direction. After the screw ring is removed from the screw portion of the one wheel shaft thereby to remove the grinding wheel from the wheel shaft in disassembling process, in assembling process a new grinding wheel is mounted on the wheel shaft and secured by the screw ring to the wheel shaft so that it needs a lot of process in the disassembling and assembling. Especially it is difficult to change the grinding wheel in so narrow area restricted by the pair of wheel shafts so that it make more difficult change the grinding wheel.